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         Portions of this Exhibit 10.4 have been redacted and are the subject of
a confidential treatment request filed with the Secretary of the Securities and
Exchange Commission.
   2
                                LICENSE AGREEMENT

This Agreement is made this 26th day of May 1998 (the "Effective Date"), by and
between the OSI Pharmaceuticals, Inc. ("OSI"), a Delaware corporation with
principal offices at 106 Charles Lindbergh Blvd., Uniondale, New York 11553-3649
and Aurora Biosciences Corporation ("ABSC"), a Delaware corporation with
principal offices at 11010 Torreyana Road, San Diego, California 92121.

                                    RECITALS

WHEREAS, OSI is the owner of the Assay Patents defined herein, and the Method of
Modulation Patents defined herein; and is willing to grant a license under such
patents to ABSC; and

WHEREAS, ABSC wishes to obtain a license under the Assay Patents and an option
to obtain a license under the Method of Modulation Patents, according to the
terms contained herein;

Now, therefore, in consideration of the covenants and premises contained herein,
the parties agree as follows:

1.       DEFINITIONS

         1.1.     "Act" is defined in Section 3.1.1.

         1.2.     "Affiliate" means any corporation or other business entity
                  controlled by or under common control with, a party to this
                  Agreement or a Third Party. Control, as used in the context of
                  a business entity, means the ownership, directly or
                  indirectly, of fifty percent (50%), or greater, or the maximum
                  interest permitted by local law of the voting securities of
                  the corporation or other entity or a fifty percent (50%) or
                  greater interest in the income of such corporation or other
                  entity or the ability otherwise to manage the affairs of such
                  corporation or other entity.

         1.3.     "Assay Patents" means the U.S. patents and patent applications
                  listed on Exhibit A hereto, any patent applications filed
                  prior or subsequent to the Effective Date that claim the
                  benefit of the filing date of any patent application listed in
                  Exhibit A and any reissues, extensions, substitutions,
                  confirmations, re-registrations, re-examinations,
                  continuations, divisionals or continuations-in-part of the
                  foregoing patents and patent applications, as well as all
                  foreign counterparts thereof, to the extent that such patents
                  and patent applications are not Method of Modulation Patents.

         1.4.     "Aurora Assay" means **  .

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         treatment.
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         1.5.     "Aurora Technology" means all Technology owned or controlled
                  by ABSC which is not an Aurora Assay.

         1.6.     "Confidential Information" means all information received by
                  either party from the other party pursuant to this Agreement,
                  which is deemed confidential by the disclosing party and is
                  designated confidential at the time the information is
                  disclosed, subject to the exceptions set forth in Section 8.1.

         1.7.     "Cosmeceuticals" means compounds, or assays for discovering
                  compounds, useful for (a) stimulation or control of hair
                  growth, (b) prevention or reversal of wrinkling of the skin,
                  or (c) alteration of skin or hair pigmentation, in each case
                  in human subjects.

         1.8.     "FDA" means the United States Food and Drug Administration, or
                  any successor agency having regulatory jurisdiction over the
                  manufacture, distribution and sale of drugs in the United
                  States or the equivalent agency in any other country.

         1.9.     "IND" means an Investigational New Drug application in the
                  United States or the equivalent application in any other
                  country.

         1.10.    "Intellectual Property" means any information and data which
                  is not generally known to the public, any new and useful
                  process, machine, manufacture, or composition of matter, or
                  improvement thereto, whether or not patentable, designs,
                  concepts, algorithms, formulae, software, techniques,
                  practices, processes, methods, knowledge, skill, experience,
                  expertise and technical information; copyrights; trade
                  secrets; or patent rights (including pending and issued patent
                  rights anywhere in the world).

         1.11.    "Materials" means any biological or chemical entity for
                  screening or assays, including reagents, cells, promoters,
                  enhancers, vectors, plasmids, proteins and fragments thereof,
                  peptides, antigens, antibodies, antagonists, agonists,
                  inhibitors, and chemicals.

         1.12.    "Method of Modulation Patents" means the U.S. patents and
                  patent applications listed on Exhibit A hereto, any patent
                  applications filed prior or subsequent to the Effective Date
                  that claim the benefit of the filing date of any patent
                  application listed in Exhibit A, and any reissues, extensions,
                  substitutions, confirmations, re-registrations,
                  re-examinations, continuations, divisionals or
                  continuations-in-part of the foregoing patents and patent
                  applications, as well as all foreign counterparts thereof, to
                  the extent such patents and patent applications claim an in
                  vivo method of modulation of a gene of interest or a
                  composition useful in such a method.

         1.13.    "NDA" means a New Drug Application or Product License
                  Application, as appropriate in the United States or the
                  equivalent application in any other country.


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         1.14.    "Net Sales" means the gross amounts actually received by ABSC
                  and its Affiliate and Sublicensees and their Affiliates from
                  arms' length sales of Product(s) to Third Parties whether
                  invoiced or not, less:

                  (i)      Trade, quantity and cash discounts allowed;

                  (ii)     Refunds, rebates, chargebacks, retroactive price
                           adjustments, and any other allowances which
                           effectively reduce the net selling price and are
                           appropriately deducted from sales under generally
                           accepted accounting principles;

                  (iii)    Product returns and allowances;

                  (iv)     Any tax imposed on the Product that is appropriately
                           deducted from sales under generally accepted
                           accounting principles;

                  (v)      That portion of the amount received associated with
                           mechanical drug delivery devices; and

                  (vi)     Allowance for distribution expenses.

                  Such amounts shall be determined from the books and records of
                  ABSC and its Affiliates and Sublicensees and their Affiliates,
                  as appropriate, maintained in accordance with generally
                  accepted accounting principles ("GAAP"), consistently applied.

                  In the event a Product is sold in combination with another
                  product(s), the Net Sales from the combination product, for
                  the purposes of determining royalty payments, shall be
                  determined by multiplying the Net Sales of the combination
                  product by the fraction, A/(A+B) where A is the average sale
                  price of the Product when sold separately and B is the average
                  sale price of the other product(s) when sold separately in
                  finished form. In the event that such average sale price
                  cannot be determined for either the Product or other
                  product(s) in such combination product, Net Sales for purposes
                  of determining royalty payments shall be calculated by
                  multiplying the Net Sales of the combination product by the
                  fraction C/(C+D) where C is the cost of manufacturing the
                  Product and D is the cost of manufacturing the other
                  product(s), determined in accordance with GAAP, consistently
                  applied.

         1.15.    "Product" means any human pharmaceutical product sold by ABSC
                  and/or an Affiliate of ABSC to a Third Party, the manufacture,
                  use, importation or sale of which in a specific country would
                  in the absence of this Agreement infringe an issued or granted
                  claim in a Method of Modulation Patent in such country and
                  which was discovered or developed by an activity which in the
                  absence of a license would infringe an issued or granted claim
                  in an Assay Patent.

         1.16.    "Shares" is defined in Section 3.1.1.

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         1.17.    "Sublicensee" means a Third Party and its Affiliates (if any)
                  that obtain a sublicense from ABSC under the Assay Patents or
                  the Method of Modulation Patents, or both.

         1.18.    "Target" means a specific gene.

         1.19.    "Technology" means Materials, Intellectual Property, or both.

         1.20.    "Term" has the meaning set forth in Section 9.1.1.

         1.21.    "Third Party" means any entity other than (i) ABSC and any of
                  its Affiliates and (ii) OSI and any of its Affiliates.

2.       LICENSES

         2.1.     Licenses Under the Assay Patents.

                  2.1.1.   OSI hereby grants to ABSC and its Affiliates**

                  2.1.2.   OSI hereby grants to ABSC and its Affiliates**


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         **  This portion has been redacted pursuant to a request
             for confidential treatment.


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                  2.1.3.   Within 30 days after the end of each calendar quarter
                           so long as this Agreement is in effect, ABSC shall
                           provide to OSI for such calendar quarter a written
                           quarterly report which indicates the following: (i)**
                           (ii) the date of **; and (iii) **.

                  2.1.4.   OSI agrees **.

         2.2.     Right to Grant Sublicenses Under the Assay Patents.

                  2.2.1.   OSI hereby grants to ABSC **.


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                                       5
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                  2.2.2.   Sublicenses under Section 2.2.1 may be granted by
                           ABSC**

                  2.2.3.   Commencing on the Effective Date, sublicenses under
                           Section 2.2.1. may be granted by ABSC**

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                                       6
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                  2.2.4.   Within 30 days after the Effective Date ABSC**

                  2.2.5.   ABSC shall within 30 days after entering into any
                           sublicense provide to OSI a copy thereof; provided,
                           however**

         2.3.     Option to Obtain A License Under the Methods of Modulation
                  Patents.

                  2.3.1.   Subject to Section 5, OSI hereby grants to ABSC and
                           its Affiliates**

                  2.3.2.   ABSC may**

                  2.3.3.   If ABSC**

                  2.3.4.   To the extent that OSI has** Exhibit C within 12
                           months of the Effective Date Exhibit C will be
                           limited to the lesser 

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   9
                           number** so listed; provided, however, that
                           if ABSC grants a sub-license**

                  2.3.5.   With respect to any Target listed on Exhibit C which
                           OSI licenses to a Third Party on at least a
                           coexclusive basis OSI will notify ABSC within 30 days
                           of granting such license that such Target is no
                           longer available for licensing to ABSC or any other
                           Third Party.

                  2.3.6.   If prior to OSI's granting at least a coexclusive
                           license to a Third Party under the Method of
                           Modulation Patents with respect to any Target listed
                           on Exhibit C, ABSC notifies OSI that ABSC wishes to
                           obtain a license with respect to such Target, OSI
                           agrees to negotiate with ABSC using good faith
                           efforts the terms of a nonexclusive license with
                           respect to such Target.

         2.4.     Right To Grant Sublicenses Under The Method of Modulation
                  Patents.

                  2.4.1.   Subject to Section 5, OSI hereby grants ABSC**

                  2.4.2.   Sublicenses under Section 2.4.1. may be granted by
                           ABSC**

                  2.4.3.   ABSC shall within 30 days after entering into any
                           sublicense under the Method of Modulation Patents
                           provide to OSI a copy thereof.

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     treatment.

                                       8
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         2.5.     Right To Require OSI To Grant Direct Licenses Under Method of
                  Modulation Patents.

                  2.5.1.   Subject to Section 5, OSI hereby agrees**

                  2.5.2.   OSI will grant direct licenses pursuant to Section
                           2.5.1. to any Third Party to which ABSC has granted a
                           sublicense under the Assay Patents pursuant to
                           Section 2.2.1. for (i) the specific Target which was
                           the subject of a sublicense under the Assay Patents
                           limited to a specific Target or (ii) any specific
                           Target if such sublicense under the Assay Patents was
                           unlimited as to the number of Targets; provided such
                           Third Party accepts and signs such direct license
                           prior to the date on which such Third Party commences
                           good laboratory practice preclinical development of a
                           compound which affects such specific Target and which
                           has resulted from such Third Party's use of Aurora
                           Technology or an Aurora Assay.

                  2.5.3.   In addition to those Third Parties to which OSI will
                           grant direct licenses as provided in Section 2.5.2.,
                           OSI will grant direct licenses for a specific target
                           pursuant to Section 2.5.1. to any Third Party for
                           whose benefit ABSC or an Affiliate of ABSC uses, but
                           to whom ABSC and Affiliates of ABSC do not transfer,
                           an Aurora Assay for such specific Target; provided
                           such Third Party accepts and signs such direct
                           license prior to the date on which such Third Party
                           commences good laboratory practice preclinical
                           development of a compound which affects such specific
                           Target and which has resulted from use of Aurora
                           Technology or an Aurora Assay by ABSC or an Affiliate
                           of ABSC.

                  2.5.4.   The financial terms of any direct license granted to
                           such Third Party pursuant to Section 2.5.1. shall be
                           the same and the nonfinancial terms thereof shall be
                           substantially the same as those of a sublicense
                           authorized pursuant to Section 2.4.1.


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                                       9
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                  2.5.5.   If a Third Party otherwise eligible to receive a
                           direct license from OSI pursuant to Section 2.5.1.
                           fails to accept and sign such a direct license with
                           respect to any Target within the time period provided
                           under Section 2.5.2. or 2.5.3., the obligation of OSI
                           to grant such a direct license shall expire with
                           respect to such Target.

                  2.5.6.   If prior to OSI's granting at least a coexclusive
                           license to a Third Party under the Method of
                           Modulation Patents with respect to any Target listed
                           on Exhibit C, ABSC notifies OSI that ABSC wishes OSI
                           to grant a direct license with respect to such Target
                           to a Third Party to which ABSC has granted a
                           sublicense under the Assay Patents for such Target,
                           OSI agrees to negotiate with such Third Party using
                           good faith efforts the terms of a nonexclusive
                           license with respect to such Target.

         2.6.     Right To Require OSI To Grant Direct Licenses Under Assay
                  Patents

                  2.6.1.   OSI hereby agrees **

                  2.6.2.   OSI will grant such direct licenses to any Third
                           Party and its Affiliates to which ABSC may grant a
                           sublicense subject to the applicable time limit and
                           in accordance with the terms of ABSC's right to grant
                           sublicenses under the Assay Patent pursuant to
                           Section 2.2. Compensation to OSI will be the same as
                           set forth in Section 3.2; provided, however that ABSC
                           will not receive or owe any payment for direct
                           licenses granted by OSI.


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3.       COMPENSATION

         3.1.     Compensation for the License Under the Assay Patents.

                  3.1.1.   As full consideration for the license granted to ABSC
                           pursuant to Section 2.1.1. herein, ABSC shall on the
                           Effective Date a) pay to OSI a non-refundable payment
                           of $50,000 and b) irrevocably issue to OSI an
                           aggregate of seventy five thousand (75,000) shares of
                           ABSC's common stock (the "Shares"). Such Shares will
                           be tradeable one year from the Effective Date,
                           subject to applicable securities laws. All
                           certificates representing the Shares shall have
                           endorsed thereon legends in substantially the
                           following forms: (i) the securities represented by
                           this certificate have not been registered under the
                           Securities Act of 1933, as amended (the "Act") and
                           they may not be sold or offered for sale or otherwise
                           distributed unless the securities are registered
                           under the Act or an exemption therefrom is available
                           and (ii) any other legend required to be placed
                           thereon by applicable state, federal or foreign
                           securities laws. OSI acknowledges that it is aware
                           that the Shares have not been registered under the
                           Act and that the Shares are deemed to constitute
                           "restricted securities" under Rule 144 under the Act.
                           No royalties or milestones or additional target fees
                           will be due pursuant to the license under Section
                           2.1.1. except as provided therein.

                  3.1.2.   As full consideration for (i) ABSC's option under
                           Section 2.3., (ii) ABSC's right to grant sublicenses
                           under Section 2.4., and (iii) ABSC's right to require
                           OSI to grant direct licenses under Section 2.5., ABSC
                           will pay to OSI a payment of two hundred and fifty
                           thousand dollars ($250,000) within thirty (30) days
                           of the Effective Date and annual payments of **, each
                           such annual payment being due on each anniversary of
                           the Effective Date. The initial $250,000 payment made
                           under this Section 3.1.2. shall be creditable against
                           the first $250,000 which ABSC is obligated to pay OSI
                           pursuant to Sections 3.2. and 3.4.

         3.2.     Compensation for Sublicenses Under The Assay Patents.

                  3.2.1.   For each sublicense granted by ABSC under Section
                           2.2., for a specific Target, ABSC will pay to OSI
                           each year commencing on the effective date of such
                           sublicense and on each anniversary date thereafter
                           that such sublicense is in effect, the greater of **
                           or ** of all sublicense income received by ABSC
                           pursuant to Section 3 of such sublicense. OSI agrees
                           and acknowledges that ABSC shall retain for itself
                           the remainder of the sublicense income, either ** or
                           ** of such sublicense income each year.


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                  3.2.2.   For each sublicense granted by ABSC under Section
                           2.2. for an unlimited number of Targets, ABSC will
                           pay to OSI each year commencing on the effective date
                           of such sublicense and on each anniversary date
                           thereafter that such sublicense is in effect, the
                           greater of (i) ** or (ii) ** of all sublicense income
                           received by ABSC pursuant to Section 3 of such
                           sublicense. OSI agrees and acknowledges that ABSC
                           shall retain for itself the remainder of the
                           sublicense income, either ** or ** of such sublicense
                           income each year.

         3.3.     Compensation for Licenses Under the Method of Modulation
                  Patents.

                  3.3.1.   For each license granted to ABSC pursuant to Section
                           2.3., ABSC will pay OSI each year commencing on the
                           effective date of such license and on each
                           anniversary date thereafter that such license is in
                           effect, an annual license fee of ** on a Target by
                           Target basis.

                  3.3.2.   For the first Product directed against each such
                           Target that reaches the following milestone events
                           and for which ABSC has a license pursuant to Section
                           2.3., ABSC will pay OSI within 30 days of such
                           milestone event the following amounts:

                                    Milestone Event                Payment (US$)

                           i)   Upon filing an IND with the FDA         **

                           ii)  Upon acceptance of the filing of 
                                an NDA by the FDA                       **
                                

                  3.3.3.   For each Target for which ABSC is granted a license
                           pursuant to Section 2.3. only one payment will be
                           required for each such milestone event regardless of
                           the number of Products directed against such Target
                           for which ABSC achieves such milestone events.

                  3.3.4.   For each Product directed against each Target for
                           which ABSC has been granted a license pursuant to
                           Section 2.3., ABSC will also pay to OSI a royalty of
                           ** of Net Sales of all such Products sold by ABSC and
                           its Affiliates on a country by country basis. If a
                           human pharmaceutical product is made, used and sold
                           in a country where no Method of Modulation Patent
                           exists, it is not a Product for purposes of this
                           agreement and no royalty is due on its sale.

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         3.4.     Compensation for Sublicenses Under the Method of Modulation
                  Patents.

                  3.4.1.   For each sublicense granted by ABSC pursuant to
                           Section 2.4.1., ABSC will pay to OSI each year
                           commencing on the effective date of such sublicense
                           and on each anniversary date thereafter that such
                           sublicense is in effect, for each specific Target for
                           which a sublicense is granted the greater of (i) **
                           or (ii) ** of the sublicense fees received by ABSC
                           pursuant to Section 3 of each such sublicense. OSI
                           agrees and acknowledges that ABSC shall retain for
                           itself the remainder of the sublicense fees, either
                           ** or ** of such sublicense fees each year.

                  3.4.2.   For the first Product directed against each such
                           Target that reaches the following milestone events
                           and for which ABSC has granted a sublicensee pursuant
                           to Section 2.4., ABSC will also pay OSI within 30
                           days of such milestone event the following amounts:

                                    Milestone Event                Payment (US$)

                           i)   Upon filing an IND with the FDA          **

                           ii)  Upon acceptance of the filing of 
                                an NDA by the FDA                        **
                                

                  3.4.3.   For each Target for which a sublicense is granted to
                           a specific Third Party as Sublicensee pursuant to
                           Section 2.4., only one payment will be required for
                           each such milestone event, regardless of the number
                           of Products directed against such Target for which
                           such Sublicensee achieves such milestone events.

                  3.4.4.   For each Product directed against each Target for
                           which ABSC has granted a sublicense pursuant to
                           Section 2.4., ABSC will also pay to OSI a royalty of
                           ** of Net Sales of all such Products sold by each
                           such Sublicensee and its Affiliates on a country by
                           country basis. If a human pharmaceutical product is
                           made, used and sold in a country where no Method of
                           Modulation Patent exists, it is not a Product for
                           purposes of this agreement and no royalty is due on
                           its sale.

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                  3.4.5.   OSI agrees and acknowledges that ABSC shall retain
                           for itself any amounts paid to it by a Sublicensee in
                           excess of the amounts that it is required to pay OSI
                           pursuant to this Section 3.4.

4.       ROYALTY PAYMENTS

         4.1.     Royalties payments due from ABSC to OSI shall be paid within
                  sixty (60) days after the end of each calendar quarter during
                  which the royalty payment accrued. Each such payment shall be
                  accompanied by a statement certified by an officer of ABSC
                  with respect to each country indicating the amount of the
                  payment, the total Net Sales of each Product sold in the
                  country and the amount of royalty due.

         4.2.     To the extent that it is lawful and practicable to do so, ABSC
                  shall make all royalty payments required under this Agreement
                  in the United States of America in U.S. Dollars. The royalty
                  payments due on each sale made outside the United States in a
                  currency other than U.S. Dollars shall be translated at the
                  rate of exchange at which U.S. Dollars are legally obtainable
                  at Citibank, N.A. in New York, New York, United States of
                  America, for the currency of the country in which the royalty
                  payment is accrued on the last business day of the calendar
                  month in which the sale was made. ABSC shall not be required
                  to make any royalty payment in contravention of the laws of
                  any country, nor shall ABSC be required to make the royalty
                  payment in the United States of America if ABSC is unable to
                  recoup the amount of such royalty or sublicense payment
                  directly or indirectly from the country in which the sales on
                  which such payment is based are made. In each country where
                  the local currency is blocked and cannot be removed from the
                  country, ABSC shall, at OSI's request, pay the royalty payment
                  accrued in each such country to OSI in local currency by
                  deposit to OSI's account at a local bank designated by OSI.

         4.3.     ABSC shall keep full and true books of account and records of
                  all sales of Product and Net Sales attributable to sales by
                  ABSC and its Affiliates. OSI shall have the right, at OSI's
                  expense, through an independent accountant reasonably approved
                  by ABSC to examine such books and records at any reasonable
                  time during business hours after notifying ABSC of its desire
                  to do so. Such examination shall be conducted no more often
                  than once each year and shall cover no more than the 3
                  preceding years. Such independent accountant shall report only
                  on the accuracy of such books and records and the reports
                  based thereon and shall not disclose specific entries to OSI.

5.       RENEGOTIATION OF TERMS FOR FUTURE LICENSES AND SUBLICENSES UNDER THE
         METHOD OF MODULATION PATENTS.

         5.1.     Commencing with the ** of the Effective Date ABSC's rights to
                  (i) exercise the option provided in Section 2.3., (ii) grant
                  sublicenses in accordance 

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                  with Section 2.4., or (iii) require OSI to grant direct
                  licenses in accordance with Section 2.5. shall renew
                  thereafter as set forth below. So long as OSI has not granted
                  any naked, nonexclusive license under the Method of Modulation
                  Patents to a Third Party, ABSC's foregoing rights shall renew
                  on the same Terms as set forth in Sections 2.3., 2.4. and 2.5.
                  If prior to the ** of the Effective Date OSI has granted at
                  least one naked, nonexclusive license under the Method of
                  Modulation Patents to a Third Party, without or without a
                  right to grant further sublicenses, OSI shall 60 days prior to
                  such ** notify ABSC in writing as to the terms of whichever
                  such license are least favorable to OSI. ABSC shall thereafter
                  have the option, by notifying OSI in writing within 60 days of
                  receiving OSI's notification of such terms, to either
                  substitute such terms for those set forth herein for new
                  licenses or terminate its rights under Sections 2.3., 2.4. and
                  2.5. So long as ABSC does not terminate its rights under
                  Sections 2.3., 2.4. and 2.5. as of the ** or any subsequent
                  anniversary of the Effective Date, OSI 60 days prior to each
                  subsequent anniversary shall notify ABSC in writing as to the
                  terms of whichever then-existing, naked nonexclusive
                  sublicense under the Method of Modulation Patents is least
                  favorable to OSI. ABSC shall thereafter have the option, by
                  notifying OSI in writing within 60 days of receiving OSI's
                  notification of such terms, to either substitute such terms
                  for those set forth herein for new licenses or to terminate
                  its rights under Sections 2.3., 2.4 and 2.5. For purposes of
                  this Section 5.1., "naked, nonexclusive license" means a
                  license granted by OSI under the Method of Modulation Patents
                  in a transaction which only involves financial consideration
                  for such license. As such a naked, nonexclusive license
                  excludes transactions involving research, development, or
                  marketing collaborations as well as those involving
                  consideration in the form of non-publicly traded equity. OSI
                  and ABSC each acknowledge that the terms applicable to
                  Sections 2.3., 2.4. and 2.5. after the ** of the Effective
                  Date may be greater than, the same as, or less than, those set
                  forth in this Agreement as of the Effective Date.

         5.2.     OSI and ABSC agree that all licenses and sublicenses granted
                  before ABSC notifies OSI that it is exercising its option to
                  substitute other terms for those then applicable shall
                  continue to be subject to the terms under which such licenses
                  or sublicenses were granted. Such other terms shall apply only
                  to licenses and sublicenses granted subsequent to such
                  notification by ABSC.

         5.3.     ABSC shall have the right, at ABSC's expense, through an
                  independent accountant reasonably approved by OSI to examine
                  all naked, nonexclusive licenses granted by OSI under the
                  Method of Modulation Patents at any reasonable time during
                  business hours after notifying OSI of its desire to do so for
                  the sole purpose of verifying that OSI has notified ABSC
                  pursuant to Section 5.1. as to the terms of whichever such
                  license are least favorable to OSI. Such examination shall be
                  conducted no more often than once each year. Such independent
                  accountant shall only verify that OSI has notified ABSC as to
                  the 

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                                       15
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                  terms of whichever such license are least favorable to OSI but
                  shall not disclose other specific details of such licenses to
                  ABSC.

6.       PROTECTION AND MAINTENANCE OF PATENT RIGHTS

         6.1.     OSI shall have complete control, at its expense and within its
                  sole discretion, over the prosecution, maintenance and
                  enforcement of the Assay Patents and the Method of Modulation
                  Patents. OSI will provide ABSC and any Sub-Licensee of ABSC
                  with written updates on the status of the prosecution of the
                  Assay Patents and the Method of Modulation Patents at least
                  once per year.

7.       REPRESENTATIONS AND WARRANTIES

         7.1. Representations and Warranties of ABSC and OSI.

                  As of the Effective Date each party hereby represents and
                  warrants:

                  Corporate Power. Such party is duly organized and validly
                  existing and in good standing under the laws of the state of
                  its incorporation and has all requisite corporate power and
                  authority to enter into this Agreement and to carry out the
                  provisions hereof.

                  Due Authorization. Such party is duly authorized to execute
                  and deliver this Agreement and to perform its obligations
                  hereunder.

                  Binding Agreement. This Agreement is a legal and valid
                  obligation binding upon it and enforceable in accordance with
                  its terms. The execution, delivery and performance of this
                  Agreement by such party does not conflict with any agreement,
                  instrument or understanding, oral or written, to which it is a
                  party or by which it may be bound, nor violate any law or
                  regulation of any court, governmental body or administrative
                  or other agency having jurisdiction over it.

                  Patents. Each party acknowledges and agrees that nothing in
                  this Agreement shall be construed as a warranty or
                  representation (i) as to the validity of any claim of an Assay
                  Patent or Method of Modulation Patent or (ii) that any Product
                  is, or will be, free from infringement of patents of Third
                  Parties.

         7.2.     Representations and Warranties of ABSC.

                  As of the Effective Date ABSC further represents and warrants
                  to OSI:

                  Authorization. All corporate action on the part of ABSC, its
                  officers, directors and stockholders necessary for the
                  authorization, issuance and delivery of the Shares pursuant to
                  Section 3 of this Agreement has been taken.

                                       16
   18
                  Valid Issuance of the Stock. The Shares, when delivered in
                  accordance with the terms herein, will be duly and validly
                  issued, fully paid and non-assessable, and will be free of any
                  liens and encumbrances.

         7.3.     Representations and Warranties of OSI.

                  As of the Effective Date OSI further represents and warrants
                  to ABSC:

                  Right to License or Sublicense. It owns all right, title and
                  interest in and to the Assay Patents and the Method of
                  Modulation Patents licensed or subject to being licensed or
                  sublicensed hereunder.

                  Patents. It has provided to ABSC a copy of each of the Assay
                  Patents and the Method of Modulation Patents issued or
                  pending. It has not granted, and during the term of this
                  Agreement will not grant, any right or interest in the Assay
                  Patents and the Method of Modulation Patents that is
                  inconsistent with the rights granted, or subject to being
                  granted, to ABSC or a Sublicensee herein. There are no
                  threatened or pending suits, claims, or proceedings including
                  interferences or opposition proceedings relating to the Assay
                  Patents and the Method of Modulation Patents, other than
                  normal patent prosecution proceedings. It does not own or hold
                  license rights to any patent or patent application not
                  included in Assay Patent and Method of Modulation Patents
                  which claims the same subject matter as that claimed therein.

                  Stock. OSI is obtaining the Shares for OSI's own account. OSI
                  has no present intention of distributing or selling said
                  Shares except as permitted under the Act. OSI is an
                  "accredited investor" as such term is defined in Rule 501
                  under the Act. OSI acknowledges and agrees the Shares may not
                  be sold, offered for sale, pledged, hypothecated or otherwise
                  transferred in the absence of an effective registration
                  statement under the Act with respect to such Shares or an
                  opinion of counsel reasonably acceptable to the Company that
                  such registration is not required.

         7.4.     Covenant Of OSI.

                  7.4.1.   OSI covenants not to sue ABSC and its Affiliates for
                           infringement of a claim of a Method of Modulation
                           Patent based upon any activity by ABSC or its
                           Affiliates prior to the date on which ABSC or an
                           Affiliate of ABSC commences good laboratory practice
                           preclinical development of a compound which affects a
                           Target; provided that ABSC and its Affiliates prior
                           to such date exercise the option pursuant to Section
                           2.3.1. and take a license under the Method of
                           Modulation Patents or discontinue all activity, in
                           either instance with respect to such Target.

                                       17
   19
                  7.4.2.   OSI covenants not to sue any Third Party to which
                           ABSC transfers Aurora Technology or an Aurora Assay
                           for infringement of a claim of an Assay Patent based
                           upon any activity by such Third Party with respect to
                           a Target prior to the date 60 days after such Third
                           Party commences a use of such Aurora Technology or
                           Aurora Assay which in the absence of a license under
                           the Assay Patent would constitute an infringement
                           thereof; provided that such Third Party prior to such
                           date obtains a license under the Assay Patents or
                           discontinues all otherwise infringing activity, in
                           each case with respect to such Target.

                  7.4.3.   OSI covenants not to sue any Third Party to which
                           ABSC has granted a sublicense under the Assay Patents
                           with respect to a Target pursuant to Section 2.2. for
                           infringement of a claim of a Method of Modulation
                           Patent based upon any activity by such Third Party
                           the date on which such Third Party commences good
                           laboratory practice preclinical development of a
                           compound which affects such Target; provided that
                           such Third Party prior to such date obtains a license
                           under the Method of Modulation Patents or
                           discontinues all activity, in either instance with
                           respect to such Target.

                  7.4.4.   If OSI should in the future acquire rights to any
                           patent which claims the same subject matter as that
                           claimed in the Assay Patents and the Method of
                           Modulation Patents, OSI covenants not to sue ABSC and
                           its Affiliates and Sublicensees for infringement of
                           such patent; provided that the licenses and
                           sublicenses granted pursuant to this Agreement are
                           then, and remain thereafter, in full force and
                           effect.

8.       CONFIDENTIALITY

         8.1.     Confidential Information. Except as expressly provided herein,
                  the parties agree that, for the Term and five (5) years
                  thereafter, the receiving party shall keep completely
                  confidential and shall not publish or otherwise disclose to
                  another party and shall not use for any purpose other than to
                  perform the purposes contemplated by this Agreement any
                  Confidential Information furnished to it by the disclosing
                  party hereto pursuant to this Agreement, except to the extent
                  that it can be established by the receiving party by competent
                  proof that such Confidential Information:

                  (i)      was already known to the receiving party, other than
                           under an obligation of confidentiality, at the time
                           of disclosure;
                  
                  (ii)     was generally available to the public or otherwise
                           part of the public domain at the time of its
                           disclosure to the receiving party;

                  (iii)    became generally available to the public or otherwise
                           part of the public domain after its disclosure and
                           other than through any act or omission of the
                           receiving party in breach of this Agreement;

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                  (iv)     was lawfully disclosed to the receiving party by a
                           person other than a party hereto, or

                  (v)      was independently developed by the receiving party.

         8.2.     Permitted Use and Disclosures. Each party hereto may use or
                  disclose Confidential Information disclosed to it by the other
                  party to the extent such use or disclosure is reasonably
                  necessary in filing or prosecuting patent applications,
                  prosecuting or defending litigation, complying with applicable
                  law, governmental regulation or court order, submitting
                  information to tax or other governmental authorities, making a
                  permitted sublicense or otherwise exercising its rights
                  hereunder, provided that if a party is required to make any
                  such disclosure of another party's Confidential Information,
                  it will give reasonable advance notice to the latter party of
                  such disclosure and, save to the extent inappropriate in the
                  case of patent applications, will use reasonable efforts to
                  secure confidential treatment of such information prior to its
                  disclosure (whether through protective orders or otherwise).

         8.3.     Confidential Terms. Except as expressly provided herein, each
                  party agrees not to disclose any terms of this Agreement to
                  another party without the consent of the other party;
                  provided, however, each party reserves the right to make
                  reasonable disclosures as required by securities or other
                  applicable laws, or to actual or prospective investors or
                  corporate partners, or to accountants, attorneys and other
                  professional advisors on a need-to-know basis under
                  circumstances that reasonably ensure the confidentiality
                  thereof, or to the extent required by law. If such
                  Confidential Information is to become public information by
                  such disclosure the disclosing party must obtain the written
                  consent of the non-disclosing party in order to obtain
                  protection of the Confidential Information if necessary. The
                  parties agree that the terms of any sub-license for the Assay
                  Patents or The Methods of Modulation Patents to which ABSC is
                  a party shall be Confidential Information and shall not be
                  disclosed to any Third Party without the prior written consent
                  of ABSC, such consent not to be unreasonably withheld.

         8.4.     Press Release. Notwithstanding the foregoing, the parties
                  shall agree upon a press release to announce the execution of
                  this Agreement as set forth in Exhibit E. Thereafter, OSI and
                  ABSC may each disclose to Third Parties the information
                  contained in such press release without the need for further
                  approval by the other.

9.       TERM AND TERMINATION

         9.1.     This Agreement is effective as of the Effective Date and shall
                  continue in full force and effect on a country by country
                  basis until the last expiration date of all patents
                  encompassed within Assay Patents and Method of Modulation
                  Patents. ("Term").

                                       19
   21
         9.2.     Either party shall have the right to terminate this Agreement
                  at any time for a material breach of this Agreement by the
                  other party, provided that the nonbreaching party shall have
                  first given ninety (90) days prior written notice to the
                  breaching party describing such breach and stating the
                  nonbreaching party's intention to terminate this Agreement if
                  such breach remains uncured, and the breaching party
                  thereafter fails to cure such breach within such 90 days.

         9.3.     ABSC's obligation to make annual payments to OSI pursuant to
                  Section 3.1.2. shall continue until the expiration date of the
                  last Method of Modulation Patent to expire; provided that if
                  ABSC terminates its rights under Sections 2.3., 2.4. and 2.5.
                  pursuant to Section 5.1. ABSC's obligations to make such
                  payments shall cease following the date of any such
                  termination of rights by ABSC.

         9.4.     ABSC's obligation to make payments to OSI pursuant to Section
                  3.2. for each such sublicense shall commence upon the grant of
                  each sublicense granted under the Assay Patents to a Third
                  Party and shall continue until the earlier of the expiration
                  date of the last Assay Patent to expire or the termination of
                  such sublicense.

         9.5.     ABSC's obligation to make payments to OSI pursuant to Section
                  3.3., for each license granted pursuant to Section 2.3., shall
                  commence upon the grant of each such license granted to ABSC
                  for a specific Target under the Method of Modulation Patents
                  and shall continue until the expiration date of the last
                  Method of Modulation Patent to expire; provided that if ABSC
                  shall have terminated such license by giving OSI six months'
                  notice of termination and shall have discontinued all activity
                  with respect to such Target ABSC obligation to make payments
                  to OSI pursuant to Section 3.3. shall thereafter cease.

         9.6.     ABSC's obligation to make payments to OSI pursuant to Section
                  3.4., for each sublicense granted pursuant to Section 2.4.,
                  shall commence upon the grant of each such sublicense granted
                  by ABSC to a Sublicensee for a specific Target under the
                  Method of Modulation Patents and shall continue until the
                  earlier of the expiration date of the last Method of
                  Modulation Patent to expire or the termination of such
                  sublicense.

         9.7.     Termination of this Agreement shall not terminate either
                  party's obligations under Section 8, ABSC's obligations to pay
                  fees, royalties and sublicensing income that have accrued
                  prior to such termination or ABSC's obligations under Sections
                  4 and 10.3.

10.      MISCELLANEOUS

         10.1.    Binding Effect; Assignment. This Agreement shall be binding
                  upon the parties' respective successors and permitted assigns.
                  Neither party may assign this Agreement or any of its rights
                  or obligations hereunder without the prior written 


                                       20
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                  consent of the other party (not to be unreasonably withheld)
                  except that either party may assign this Agreement as part of
                  a merger or consolidation in which the surviving entity
                  assumes all of the party's rights and obligations hereunder or
                  a sale of substantially all of the assets of such party to
                  which this Agreement relates.

         10.2.    Effect of Waiver. No waiver of any default, condition,
                  provisions or breach of this Agreement shall be deemed to
                  imply or constitute a waiver of any other default, condition,
                  provision or breach of this Agreement.

         10.3.    Indemnification. Each of OSI and ABSC shall indemnify and hold
                  the other harmless with respect to any injury, loss or cost
                  resulting from the breach of any representation or warranty
                  provided pursuant to Section 7.0. Further, ABSC shall
                  indemnify and hold OSI harmless with respect to any injury,
                  loss or cost resulting from the clinical testing of compounds
                  and the manufacture, use or sale of Products by ABSC and its
                  Affiliates.

         10.4.    Force Majeure. Neither party shall lose any rights hereunder
                  or be liable to the other party for damages or losses (except
                  for payment obligations) on account of failure of performance
                  by the defaulting party if the failure is occasioned by war,
                  strike, fire, acts of God, earthquake, flood, lockout,
                  embargo, governmental acts or orders or restrictions, failure
                  of suppliers, or any other reason where failure to perform is
                  beyond the reasonable control and not caused by the negligence
                  or intentional conduct or misconduct of the nonperforming
                  party, and such party has exerted all reasonable efforts to
                  avoid or remedy such force majeure; provided, however, that in
                  no event shall a party be required to settle any labor dispute
                  or disturbance.

         10.5.    Amendment. No modification, supplement to or waiver of this
                  Agreement or any Addendum hereto or any of their provisions
                  shall be binding upon a party hereto unless made in writing
                  and duty signed by an authorized representative of both OSI
                  and ABSC.

         10.6.    Entire Agreement. This Agreement, including the Exhibits
                  attached hereto, sets forth the entire understanding and
                  agreement of the parties as to the subject matter hereof, and
                  there are no other understandings, representations or
                  promises, written or verbal, not set forth herein on which
                  either party has relied.

         10.7.    Notices. All Notices under this Agreement shall be given in
                  writing and shall be addressed to the parties at the following
                  addresses:

                           For OSI: OSI Pharmaceuticals, Inc.
                                    106 Charles Lindbergh Blvd.
                                    Uniondale, New York 11553
                                    Attn: President

                                       21
   23
                           For ABSC:        Aurora Biosciences Corporation
                                            11010 Torreyana Road
                                            San Diego, California 92121
                                            Attn: President

                  Notices shall be in writing and shall be deemed delivered when
                  received, if delivered by a courier, or on the second business
                  day following mailing, if sent by first-class certified or
                  registered mail, postage prepaid, and return receipt
                  requested.

         10.8.    Arbitration. The parties recognize that disputes as to certain
                  matters may from time to time arise during the term of this
                  Agreement which relate to either party's rights and/or
                  obligations hereunder. It is the objective of the parties to
                  establish procedures to facilitate the resolution of disputes
                  arising under this Agreement in an expedient manner by mutual
                  cooperation without resort to arbitration. The parties agree
                  that prior to any arbitration concerning this Agreement, OSI's
                  CEO and ABSC's CEO will meet in person or by
                  video-conferencing in a good faith effort to resolve any
                  disputes concerning this Agreement, such meeting to be held
                  within 30 days after notice is received by one party from the
                  other requesting such a meeting. Except as otherwise provided
                  specifically herein, any controversy or claim under this
                  Agreement except a claim as to the scope, validity or
                  enforcement of a claim of an Assay Patent or a Method of
                  Modulation Patent shall be settled solely by arbitration by
                  one arbitrator pursuant to the Commercial Arbitration Rules of
                  the American Arbitration Association (the "Association");
                  provided that the parties shall first have used their best
                  efforts to resolve such dispute by negotiation as set forth
                  above. ** The arbitrator shall be selected by the joint
                  agreement of the parties, but if they do not so agree within
                  twenty (20) days of the date of a request for arbitration, the
                  selection shall be made pursuant to the rules of the
                  Association. The decision reached by the arbitrator shall be
                  conclusive and binding upon the parties hereto and may be
                  filed with the clerk of any court of competent jurisdiction,
                  and a judgment confirming such decision may, if desired by any
                  party to the arbitration, be entered in such court. Each of
                  the parties shall pay its own expenses of arbitration and the
                  expenses of the arbitrator(s) shall be equally shared;
                  provided, however, that if in the opinion of the arbitrator(s)
                  any claim hereunder or any defense or objection thereto was
                  unreasonable, the arbitrator(s) may assess, as part of the
                  award, all or any part of the arbitration expenses (including
                  reasonable attorneys' fees) against the party raising such
                  unreasonable claim, defense or objection. Nothing herein set
                  forth shall prevent the parties from settling any dispute by
                  mutual agreement at any time.

                  10.9. Governing Law. This Agreement shall be governed by and
                  construed in accordance with the laws of the State of New
                  York, applicable to agreements 

__________

**   This portion has been redacted pursuant to a request for confidential 
     treatment.


                                       22
   24
                  made in New York without regard, or giving effect, to its
                  principles of conflict of laws.

         10.10.   Severability. This Agreement is intended to be severable. If
                  any provision(s) of this Agreement are or become invalid, are
                  ruled illegal by a court of competent jurisdiction or are
                  deemed unenforceable under the current applicable law from
                  time to time in effect during the term hereof, it is the
                  intention of the parties that the remainder of the Agreement
                  shall not be affected thereby and shall continue to be
                  construed to the maximum extent permitted by law at such time.
                  It is further the intention of the parties that in lieu of
                  each such provision which is invalid, illegal, or
                  unenforceable, there shall be substituted or added as part of
                  this Agreement by such court of competent jurisdiction a
                  provision which shall be as similar as possible in terms of
                  the economic and business objectives intended by the parties,
                  to such invalid, illegal or unenforceable provision, but shall
                  be valid, legal and enforceable.

         10.11.   Independent Contractors. The parties hereto are acting as
                  independent contractors and shall not be considered partners,
                  joint venturers or agents of the other. Except as expressly
                  provided herein, neither party shall have the right to act on
                  behalf of, or to bind, the other.

         10.12.   Headings. Captions and paragraph headings are for convenience
                  only and shall not form an interpretative part of this
                  Agreement. This Agreement shall not be strictly construed
                  against either party hereto and may be executed in two or more
                  counterparts, each of which will be deemed an original.


                                       23
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         IN WITNESS WHEREOF, the parties have executed this Agreement.



By: /s/  Colin Goddard, Ph.D.       Date:      22- May-98
   ---------------------------             -----------------
Colin Goddard, Ph.D.
President
For OSI Pharmaceuticals, Inc.


By: /s/ Paul A. Grayson             Date:     22 - May - 98
   ---------------------------             -----------------
Paul A. Grayson
Senior Vice President/Corporate Development
For Aurora Biosciences Corporation



                                       24
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                                    Exhibit A


U.S. Serial No.                 Status             Patent No. If Applicable

    **                            **                   **


- ------------------

**       This portion has been redacted pursuant to a request for confidential
         treatment.



                                       25
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                                    EXHIBIT B

                                  ASSAY PATENTS
                              SUBLICENSE AGREEMENT


This Agreement is made this _______ day of _______ (the "Effective Date"), by
and between Aurora Biosciences Corporation ("ABSC"), a Delaware corporation with
principal offices at 11010 Torreyana Road, San Diego, California 92121 and
___________________ ("Sublicensee"), a ________ corporation with principal
offices at__________________________________.

                                    RECITALS

WHEREAS, ABSC is a licensee under the Assay Patents defined herein, pursuant to
a License Agreement dated May ___, 1998 with OSI Pharmaceuticals, Inc. ("OSI"),
the assignee of the Assay Patents; and is willing to grant a sublicense under
such patents to Sublicensee; and

WHEREAS, Sublicensee wishes to obtain a sublicense from ABSC under the Assay
Patents, according to the terms contained herein;

Now, therefore, in consideration of the covenants and premises contained herein,
the parties agree as follows:

1.       DEFINITIONS

         1.1.     "Affiliate" means any corporation or other business entity
                  controlled by or under common control with, a party to this
                  Agreement. Control, as used in the context of a business
                  entity, means the ownership, directly or indirectly, of fifty
                  percent (50%), or greater, or the maximum interest permitted
                  by local law of the voting securities of the corporation or
                  other entity or a fifty percent (50%) or greater interest in
                  the income of such corporation or other entity or the ability
                  otherwise to manage the affairs of such corporation or other
                  entity.

         1.2.     "Assay Patents" means the U.S. patents and patent applications
                  listed on Exhibit A hereto, any patent applications filed
                  prior or subsequent to the Effective Date that claim the
                  benefit of the filing date of any patent application listed in
                  Exhibit A and any reissues, extensions, substitutions,
                  confirmations, re-registrations, re-examinations,
                  continuations, divisionals or continuations-in-part of the
                  foregoing patents and patent applications, as well as all
                  foreign counterparts thereof, to the extent that such patents
                  and patent applications are not Method of Modulation Patents.



                                       1
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         1.3.     "Aurora Assay" means **  .

         1.4.     "Aurora Technology" means all Technology owned or controlled
                  by ABSC which is not an Aurora Assay.

         1.5.     "Confidential Information" means all information received by
                  either party from the other party pursuant to this Agreement,
                  which is deemed confidential by the disclosing party and is
                  designated confidential at the time the information is
                  disclosed, subject to the exceptions set forth in Section 6.
                  1.

         1.6.     "Cosmeceuticals" means compounds, or assays for discovering
                  compounds, useful for (a) stimulation or control of hair
                  growth, (b) prevention or reversal of wrinkling of the skin,
                  or (c) alteration of skin or hair pigmentation, in each case
                  in human subjects.

         1.7.     "Intellectual Property" means any information and data which
                  is not generally known to the public, any new and useful
                  process, machine, manufacture, or composition of matter, or
                  improvement thereto, whether or not patentable, designs,
                  concepts, algorithms, formulae, software, techniques,
                  practices, processes, methods, knowledge, skill, experience,
                  expertise and technical information; copyrights; trade
                  secrets; or patent rights (including pending and issued patent
                  rights anywhere in the world).

         1.8.     "Materials" means any biological or chemical entity for
                  screening or assays, including reagents, cells, promoters,
                  enhancers, vectors, plasmids, proteins and fragments thereof,
                  peptides, antigens, antibodies, antagonists, agonists,
                  inhibitors, and chemicals.

         1.9.     "Method of Modulation Patents" means the U.S. patents and
                  patent applications listed on Exhibit A hereto, any patent
                  applications filed prior or subsequent to the Effective Date
                  that claim the benefit of the filing date of any patent
                  application listed in Exhibit A, and any reissues, extensions,
                  substitutions, confirmations, re-registrations,
                  re-examinations, continuations, divisionals or
                  continuations-in-part of the foregoing patents and patent
                  applications, as well as all foreign counterparts thereof, to
                  the extent such patents and patent applications claim an in
                  vivo method of modulation of a gene of interest or a
                  composition useful in such a method.

         1.10.    "Sub-Licensee" means the party so identified and first above
                  named.

         1.11.    "Target" means a specific gene.

         1.12.    "Technology" means Materials, Intellectual Property, or both.

- -----------------

**       This portion has been redacted pursuant to a request for confidential
         treatment.

                                       2
   29
         1.13.    "Term" has the meaning set forth in Section 7.1.1.

         1.14.    "Third Party" means any entity other than (i) ABSC and any of
                  its Affiliates and (ii) Sub-Licensee and any of its
                  Affiliates.

2.       SUBLICENSE

         2.1.     Sublicense Under the Assay Patents.

                  2.1.1.   Subject to any limitations as to the number and
                           identity of Targets pursuant to Section 2.1.2., ABSC
                           hereby grants to Sublicensee and its Affiliates, for
                           all fields except the field of specifically
                           discovering or developing Cosmeceuticals, a
                           nonexclusive, worldwide sublicense, without the right
                           to grant subsublicenses, under the Assay Patents (i)
                           to make or use any method, device or composition of
                           matter encompassed within, using or incorporating,
                           Aurora Technology or an Aurora Assay and (ii) to
                           make, use, have made, sell, offer for sale, import,
                           export, or otherwise exploit any compound which
                           results from the use of Aurora Technology or an
                           Aurora Assay by Sublicensee or an Affiliate of
                           Sublicensee; provided that such making, using, having
                           made, selling, offering for sale, importing,
                           exporting, or otherwise exploiting such compound
                           resulting from the use by Sublicensee or an Affiliate
                           of Sublicensee of Aurora Technology or an Aurora
                           Assay does not require a license under the Method of
                           Modulation Patents in which event a separate license
                           or sub-license under the Method of Modulation Patents
                           is required for which compensation will be due
                           pursuant to the terms of such separate license or
                           sub-license.

                           (ABSC MAY DELETE SECTION 2.1.2. IF NOT APPLICABLE ie.
                           WHEN THE SUB-LICENSE IS FOR AN UNLIMITED NUMBER OF
                           TARGETS)

                  2.1.2.   Sublicensee's sublicense granted pursuant to Section
                           2.1.1. shall be limited to the specific Target or
                           Targets set forth on Exhibit B hereto, which Targets
                           may be identified by code numbers.

                  2.1.3.   ABSC agrees that if in the future ABSC obtains rights
                           in the field of Cosmeceuticals because the field of
                           Cosmeceuticals ceases to be the subject of an
                           exclusive license grant by OSI to the Third Party
                           licensed as of the Effective Date of the License
                           Agreement between OSI and ABSC, the scope of
                           Sublicensee's nonexclusive sublicense under Section
                           2.1.1 shall be expanded to include Cosmeceuticals
                           without any additional consideration being provided
                           to ABSC by Sublicensee other than that already
                           provided for herein.

                                       3
   30
                  2.1.4.   ABSC shall within 30 days after entering into this
                           Agreement provide to OSI a copy thereof, provided,
                           however, that the specific Target(s) to which this
                           Agreement relates may be identified by code numbers
                           if the Sublicensee so desires.

3.       COMPENSATION

         3.1.     Compensation for Sublicense Under the Assay Patents.

                  (ABSC MAY DELETE WHICHEVER VERSION OF SECTION 3.1.1. IS NOT
                  APPLICABLE. MOREOVER, IN ADDITION TO THE PAYMENT SPECIFICALLY
                  PROVIDED FOR IN SECTION 3.1.1 ABSC MAY INCLUDE A PROVISION IN
                  THIS SECTION 3 FOR AN UPFRONT SUB-LICENSING FEE.)

                  3.1.1.   For each specific Target for which a sublicense is
                           granted by ABSC pursuant to Section 2.1.1. for the
                           limited number of Targets which are identified on
                           Exhibit B hereto, Sublicensee will pay to ABSC each
                           year commencing on the Effective Date of this
                           Agreement and on each anniversary date thereafter
                           that this Agreement is in effect, _________ Dollars
                           ($____________) per Target.

                  3.1.1    For each sublicense granted by ABSC under Section
                           2.1.1. for an unlimited number of Targets,
                           Sublicensee will pay to ABSC each year commencing on
                           the Effective Date of this Agreement, and on each
                           anniversary date thereafter that this Agreement is in
                           effect, _________ Dollars ($____________) per Target.

4.       PROTECTION AND MAINTENANCE OF PATENT RIGHTS

         4.1.     Sublicensee acknowledges and agrees that OSI shall have
                  complete control, at its expense and within its sole
                  discretion, over the prosecution, maintenance and enforcement
                  of the Assay Patents. ABSC directly or through OSI, will
                  provide Sublicensee with written updates on the status of the
                  prosecution of the Assay Patents at least once per year

5.       REPRESENTATIONS AND WARRANTIES

         5.1.     Representations and Warranties of ABSC and Sublicensee

                  As of the Effective Date each party hereby represents and
                  warrants:

                  Corporate Power. Such party is duly organized and validly
                  existing and in good standing under the laws of the state of
                  its incorporation and has all requisite 



                                       4
   31
                  corporate power and authority to enter into this Agreement and
                  to carry out the provisions hereof.

                  Due Authorization. Such party is duly authorized to execute
                  and deliver this Agreement and to perform its obligations
                  hereunder.

                  Binding Agreement. This Agreement is a legal and valid
                  obligation binding upon it and enforceable in accordance with
                  its terms. The execution, delivery and performance of this
                  Agreement by such party does not conflict with any agreement,
                  instrument or understanding, oral or written, to which it is a
                  party or by which it may be bound, nor violate any law or
                  regulation of any court, governmental body or administrative
                  or other agency having jurisdiction over it.

                  Patents. Each party acknowledges and agrees that nothing in
                  this Agreement shall be construed as a warranty or
                  representation (i) as to the validity of any claim of an Assay
                  Patent or (ii) that any activity by Sublicensee is, or will
                  be, free from infringement of patents of Third Parties.

         5.2.     Representations and Warranties of ABSC.

                  As of the Effective Date ABSC further represents and warrants
                  to Sublicensee that it has a license under the Assay Patents
                  and the right to grant the Sublicense being granted hereunder,
                  subject to Sublicensee's representations and warranties in
                  Section 5.3 being correct and valid.

         5.3.     Representations and Warranties of Sublicensee.

                  As of the Effective Date Sublicensee further represents and
                  warrants to ABSC and to OSI that neither Sublicensee nor any
                  Affiliate of Sublicensee commenced, more than 90 days prior to
                  the Effective Date of this Agreement, any use of Aurora
                  Technology or an Aurora Assay which, in the absence of this
                  Agreement, would have constituted an infringement of a claim
                  of an Assay Patent.

6.       CONFIDENTIALITY

         6.1.     Confidential Information. Except as expressly provided herein,
                  the parties agree that, for the Term and five (5) years
                  thereafter, the receiving party shall keep completely
                  confidential and shall not publish or otherwise disclose to
                  another party and shall not use for any purpose other than to
                  perform the purposes contemplated by this Agreement any
                  Confidential Information furnished to it by the disclosing
                  party hereto pursuant to this Agreement, except to the extent
                  that it can be established by the receiving party by competent
                  proof that such Confidential Information:

                                       5
   32
                  (i)      was already known to the receiving party, other than
                           under an obligation of confidentiality, at the time
                           of disclosure;

                  (ii)     was generally available to the public or otherwise
                           part of the public domain at the time of its
                           disclosure to the receiving party;

                  (iii)    became generally available to the public or otherwise
                           part of the public domain after its disclosure and
                           other than through any act or omission of the
                           receiving party in breach of this Agreement;

                  (iv)     was lawfully disclosed to the receiving party by a
                           person other than a party hereto, or

                  (v)      was independently developed by the receiving party.

         6.2.     Permitted Use and Disclosures. Each party hereto may use or
                  disclose Confidential Information disclosed to it by the other
                  party to the extent such use or disclosure is reasonably
                  necessary in filing or prosecuting patent applications,
                  prosecuting or defending litigation, complying with applicable
                  law, governmental regulation or court order, submitting
                  information to tax or other governmental authorities, making a
                  permitted sublicense or otherwise exercising its rights
                  hereunder, provided that if a party is required to make any
                  such disclosure of another party's Confidential Information,
                  it will give reasonable advance notice to the latter party of
                  such disclosure and, save to the extent inappropriate in the
                  case of patent applications, will use reasonable efforts to
                  secure confidential treatment of such information prior to its
                  disclosure (whether through protective orders or otherwise).

         6.3.     Confidential Terms. Except as expressly provided herein, each
                  party agrees not to disclose any terms of this Agreement to
                  another party other than OSI without the consent of the other
                  party; provided, however, each party reserves the right to
                  make reasonable disclosures as required by securities or other
                  applicable laws, or to actual or prospective investors or
                  corporate partners, or to accountants, attorneys and other
                  professional advisors on a need-to-know basis under
                  circumstances that reasonably ensure the confidentiality
                  thereof, or to the extent required by law. If such
                  Confidential Information is to become public information by
                  such disclosure the disclosing party must obtain the written
                  consent of the non-disclosing party in order to obtain
                  protection of the Confidential Information if necessary.

7.       TERM AND TERMINATION

         7.1.     Unless terminated earlier, this Agreement and Sublicensee's
                  obligations to make payments to ABSC pursuant to Section 3.1.
                  is effective as of the Effective Date and shall continue in
                  full force and effect on a country by country basis until the
                  last expiration date of all patents encompassed within the
                  Assay Patents ("Term").

         7.2.     Either party shall have the right to terminate this Agreement
                  at any time for a material breach of this Agreement by the
                  other party, provided that the 



                                       6
   33
                  nonbreaching party shall have first given ninety (90) days
                  prior written notice to the breaching party describing such
                  breach and stating the nonbreaching party's intention to
                  terminate this Agreement if such breach remains uncured, and
                  the breaching party thereafter fails to cure such breach
                  within such 90 days.

         7.3.     Sublicensee may terminate this Agreement by giving ABSC six
                  months' prior written notice of termination; provided that
                  Sublicensee shall not thereafter continue to develop, make,
                  use, have made, sell, offer for sale, import, export or
                  otherwise exploit any compound which results from a use of
                  Aurora Technology or an Aurora Assay by or on behalf of
                  Sublicensee or an Affiliate of Sublicensee and which is
                  directed against any Target embodied in such Aurora Technology
                  or Aurora Assay, if such use would in the absence of this
                  Agreement have constituted an infringement of a claim of an
                  Assay Patent. However, Sublicensee may independently develop
                  the same compound for a different Target.

         7.4.     Termination of this Agreement shall not terminate either
                  party's obligations under Section 6, Sublicensee's obligations
                  to pay fees under Section 3 that have accrued prior to such
                  termination or Sublicensee's obligations under Section 8.3.

8.       MISCELLANEOUS

         8.1.     Binding Effect: Assignment. This Agreement shall be binding
                  upon the parties' respective successors and permitted assigns.
                  Neither party may assign this Agreement or any of its rights
                  or obligations hereunder without the prior written consent of
                  the other party (not to be unreasonably withheld) except that
                  either party may assign this Agreement as part of a merger or
                  consolidation in which the surviving entity assumes all of the
                  party's rights and obligations hereunder or a sale of
                  substantially all of the assets of such party to which this
                  Agreement relates.

         8.2.     Effect of Waiver. No waiver of any default, condition,
                  provisions or breach of this Agreement shall be deemed to
                  imply or constitute a waiver of any other default, condition,
                  provision or breach of this Agreement.

         8.3.     Indemnification. Each of ABSC and Sublicensee shall indemnify
                  and hold the other and OSI harmless with respect to any
                  injury, loss or cost resulting from the breach of any
                  representation or warranty provided pursuant to Section 5.0.
                  Further, Sublicensee shall indemnify and hold ABSC and OSI
                  harmless with respect to any injury, loss or cost resulting
                  from the clinical testing of compounds, the manufacture, use
                  or sale of products by Sublicensee and its Affiliates, and any
                  other activity carried out pursuant to the right license
                  herein.

         8.4.     Force Majeure. Neither party shall lose any rights hereunder
                  nor be liable to the other party for damages or losses (except
                  for payment obligations) on account of failure of performance
                  by the defaulting party if the failure is occasioned by war,
                  strike, fire, acts of God, earthquake, flood, lockout,
                  embargo, governmental acts 



                                       7
   34
                  or orders or restrictions, failure of suppliers, or any other
                  reason where failure to perform is beyond the reasonable
                  control and not caused by the negligence or intentional
                  conduct or misconduct of the nonperforming party, and such
                  party has exerted all reasonable efforts to avoid or remedy
                  such force majeure; provided, however, that in no event shall
                  a party be required to settle any labor dispute or
                  disturbance.

         8.5.     Amendment. No modification, supplement to or waiver of this
                  Agreement or any Addendum hereto or any of their provisions
                  shall be binding upon a party hereto unless (i) made in
                  writing, (ii) duly signed by an authorized representative of
                  both ABSC and Sublicensee, and (iii) consented to by OSI, such
                  consent not to be unreasonably withheld.

         8.6.     Entire Agreement. This Agreement, including the Exhibits
                  attached hereto, sets forth the entire understanding and
                  agreement of the parties as to the subject matter hereof, and
                  there are no other understandings, representations, or
                  promises, written or verbal, not set forth herein or on which
                  either party has relied.

         8.7.     Notices. All notices under this Agreement shall be given in
                  writing and shall be addressed to the parties at the following
                  addresses:

                           For Sublicensee:



                           For ABSC:        Aurora Biosciences Corporation
                                            11010 Torreyana Road
                                            San Diego, California 92121
                                            Attn:  President


                  Copies of all notices shall be sent to OSI at the following
                  address:

                            OSI Pharmaceuticals, Inc.
                            106 Charles Lindbergh Blvd.
                            Uniondale, New York 1 1553

                            Attn:  President

                  Notices shall be in writing and shall be deemed delivered when
                  received, if delivered by a courier, or on the second business
                  day following mailing, if sent by first-class certified or
                  registered mail, postage prepaid, and return receipt
                  requested.

                                       8
   35
         8.8.     Arbitration. The parties recognize that disputes as to certain
                  matters may from time to time arise during the term of this
                  Agreement which relate to either party's rights and/or
                  obligations hereunder. It is the objective of the parties to
                  establish procedures to facilitate the resolution of disputes
                  arising under this Agreement in an expedient manner by mutual
                  cooperation without resort to arbitration. The parties agree
                  that prior to any arbitration concerning this Agreement,
                  ABSC's CEO and Sublicensees's CEO will meet in person or by
                  video-conferencing in a good faith effort to resolve any
                  disputes concerning this Agreement, such meeting to be held
                  within 30 days after notice is received by one party from the
                  other requesting such a meeting. Except as otherwise provided
                  specifically herein, any controversy or claim under this
                  Agreement except a claim as to the scope, validity or
                  enforcement of a claim of an Assay Patent or a Method of
                  Modulation Patent shall be settled solely by arbitration by
                  one arbitrator pursuant to the Commercial Arbitration Rules of
                  the American Arbitration Association (the "Association");
                  provided that the parties shall first have used their best
                  efforts to resolve such dispute by negotiation as set forth
                  above. The arbitration shall be conducted in **. The
                  arbitrator shall be selected by the joint agreement of the
                  parties, but if they do not so agree within twenty (20) days
                  of the date of a request for arbitration, the selection shall
                  be made pursuant to the rules of the Association. The decision
                  reached by the arbitrator shall be conclusive and binding upon
                  the parties hereto and may be filed with the clerk of any
                  court of competent jurisdiction, and a judgment confirming
                  such decision may, if desired by any party to the arbitration,
                  be entered in such court. Each of the parties shall pay its
                  own expenses of arbitration and the expenses of the
                  arbitrator(s) shall be equally shared, provided, however, that
                  if in the opinion of the arbitrator(s) any claim hereunder or
                  any defense or objection thereto was unreasonable, the
                  arbitrator(s) may assess, as part of the award, all or any
                  part of the arbitration expenses (including reasonable
                  attorneys' fees) against the party raising such unreasonable
                  claim, defense or objection. Nothing herein set forth shall
                  prevent the parties from settling any dispute by mutual
                  agreement at any time.

         8.9.     Governing Law. This Agreement shall be governed by and
                  construed in accordance with the laws of the State of New
                  York, applicable to agreements made in New York without
                  regard, or giving effect, to its principles of conflict of
                  laws.

         8.10.    Severability. This Agreement is intended to be severable. If
                  any provision(s) of this Agreement are or become invalid, are
                  ruled illegal by a court of competent jurisdiction or are
                  deemed unenforceable under the current applicable law from
                  time to time in effect during the term hereof, it is the
                  intention of the parties that the remainder of the Agreement
                  shall not be affected thereby and shall continue to be
                  construed to the maximum extent permitted by law at such time.
                  It is further the intention of the parties that in lieu of
                  each such provision which is invalid, illegal, or
                  unenforceable, there shall be substituted or added as part of
                  this Agreement by such court of competent jurisdiction a
                  provision which shall be as 
__________

**   This portion has been redacted pursuant to a request for confidential 
     treatment.



                                       9
   36
                  similar as possible in terms of the economic and business
                  objectives intended by the parties, to such invalid, illegal
                  or unenforceable provision, but shall be valid, legal and
                  enforceable.

         8.11.    Independent Contractors. The parties hereto are acting as
                  independent contractors and shall not be considered partners,
                  joint venturers or agents of the other. Neither party shall
                  have the right to act on behalf of, or to bind, the other.

         8.12.    Headings. Captions and paragraph headings are for convenience
                  only and shall not form an interpretative part of this
                  Agreement. This Agreement shall not be strictly construed
                  against either party hereto and may be executed in two or more
                  counterparts, each of which will be deemed an original.


                                       10
   37
         IN WITNESS WHEREOF, the parties have executed this Agreement.


 By:                                                  Date:
    -------------------------------            --------------------
Name:
Title:
For Sublicensee


 By:                                    Date:
    -------------------------------            --------------------

Timothy J. Rink M.D., Sc.D.
President, CEO and Chairman
For Aurora Biosciences Corporation


                                       11
   38
                                    EXHIBIT C

                              EXCLUDED OSI TARGETS



         **


- ------------------

**       This portion has been redacted pursuant to a request for confidential
         treatment.



                                       1
   39
                                    EXHIBIT D

                          METHOD OF MODULATION PATENTS
                              SUBLICENSE AGREEMENT



This Agreement is made this ______ day of _________ (the "Effective Date"), by
and between Aurora Biosciences Corporation ("ABSC"), a Delaware corporation with
principal offices at 11010 Torreyana Road, San Diego, California 92121 and
____________________ ("Sublicensee"), a _______ corporation with principal
offices at ____________________________.

                                    RECITALS

WHEREAS, ABSC is a licensee under the Method of Modulation Patents defined
herein, pursuant to a License Agreement dated May _, 1998 with OSI
Pharmaceuticals, Inc. ("OSI"), the assignee of the Method of Modulation Patents;
and is willing to grant a sublicense under such patents to Sublicensee; and

WHEREAS, Sublicensee wishes to obtain a sublicense from ABSC under the Method of
Modulation Patents, according to the terms contained herein;

Now, therefore, in consideration of the covenants and premises contained herein,
the parties agree as follows:

1.       DEFINITIONS

         1.1.     "Affiliate" means any corporation or other business entity
                  controlled by or under common control with, a party to this
                  Agreement. Control, as used in the context of a business
                  entity, means the ownership, directly or indirectly, of fifty
                  percent (50%), or greater, or the maximum interest permitted
                  by local law of the voting securities of the corporation or
                  other entity or a fifty percent (50%) or greater interest in
                  the income of such corporation or other entity or the ability
                  otherwise to manage the affairs of such corporation or other
                  entity.

         1.2.     "Assay Patents" means the U.S. patents and patent applications
                  listed on Exhibit A hereto, any patent applications filed
                  prior or subsequent to the Effective Date that claim the
                  benefit of the filing date of any patent application listed in
                  Exhibit A and any reissues, extensions, substitutions,
                  confirmations, re-registrations, re-examinations,
                  continuations, divisionals or continuations-in-part of the
                  foregoing patents and patent applications, as well as all
                  foreign counterparts thereof, to the extent that such patents
                  and patent applications are not Method of Modulation Patents.

                                       1
   40
         1.3.     "Aurora Assay" means  **  .

         1.4.     "Aurora Technology" means all Technology owned or controlled
                  by ABSC which is not an Aurora Assay.

         1.5.     "Confidential Information" means all information received by
                  either party from the other party pursuant to this Agreement,
                  which is deemed confidential by the disclosing party and is
                  designated confidential at the time the information is
                  disclosed, subject to the exceptions set forth in Section 7.1.

         1.6.     "Cosmeceuticals" means compounds, or assays for discovering
                  compounds, useful for (a) stimulation or control of hair
                  growth, (b) prevention or reversal of wrinkling of the skin,
                  or (c) alteration of skin or hair pigmentation, in each case
                  in human subjects.

         1.7.     "FDA" means the United States Food and Drug Administration, or
                  any successor agency having regulatory jurisdiction over the
                  manufacture, distribution and sale of drugs in the United
                  States or the equivalent agency in any other country.

         1.8.     "IND" means an Investigational New Drug application in the
                  United States or the equivalent application in any other
                  country.

         1.9.     "Intellectual Property" means any information and data which
                  is not generally known to the public, any new and useful
                  process, machine, manufacture, or composition of matter, or
                  improvement thereto, whether or not patentable, designs,
                  concepts, algorithms, formulae, software, techniques,
                  practices, processes, methods, knowledge, skill, experience,
                  expertise and technical information; copyrights; trade
                  secrets; or patent rights (including pending and issued patent
                  rights anywhere in the world).

         1.10.    "Materials" means any biological or chemical entity for
                  screening or assays, including reagents, cells, promoters,
                  enhancers, vectors, plasmids, proteins and fragments thereof,
                  peptides, antigens, antibodies, antagonists, agonists,
                  inhibitors, and chemicals.

         1.11.    "Method of Modulation Patents" means the U.S. patents and
                  patent applications listed on Exhibit A hereto, any patent
                  applications filed prior or subsequent to the Effective Date
                  that claim the benefit of the filing date of any patent
                  application listed in Exhibit A, and any reissues, extensions,
                  substitutions, confirmations, re-registrations,
                  re-examinations, continuations, divisionals or
                  continuations-in-part of the foregoing patents and patent
                  applications, as well as all foreign counterparts thereof, to
                  the extent such patents and patent applications claim an in
                  vivo method of modulation of a gene of interest or a
                  composition useful in such a method.


- ------------------ 

**       This portion has been redacted pursuant to a request for confidential
         treatment.

                                       2
   41
         1.12.    "NDA" means a New Drug Application or Product License
                  Application, as appropriate, in the United States or the
                  equivalent application in any other country.

         1.13.    "Net Sales" means the gross amounts actually received by
                  Sublicensee and its Affiliates and subsublicensees from arms'
                  length sales of Product(s) to Third Parties whether invoiced
                  or not, less:

                  (i)      Trade, quantity and cash discounts allowed;

                  (ii)     Refunds, rebates, chargebacks, retroactive price
                           adjustments, and any other allowances which
                           effectively reduce the net selling price and are
                           appropriately deducted from sales under generally
                           accepted accounting principles;

                  (iii)    Product returns and allowances;

                  (iv)     Any tax imposed on the Product that is appropriately
                           deducted from sales under generally accepted
                           accounting principles;

                  (v)      That portion of the amount received associated with
                           mechanical drug delivery devices; and

                  (vi)     Allowance for distribution expenses.

                  Such amounts shall be determined from the books and records of
                  Sublicensee and its Affiliates and subsublicensees, as
                  appropriate, maintained in accordance with generally accepted
                  accounting principles ("GAAP"), consistently applied.

                  In the event a Product is sold in combination with another
                  product(s), the Net Sales from the combination product, for
                  the purposes of determining royalty payments, shall be
                  determined by multiplying the Net Sales of the combination
                  product by the fraction, A/(A+B) where A is the average sale
                  price of the Product when sold separately and B is the average
                  sale price of the other product(s) when sold separately in
                  finished form. In the event that such average sale price
                  cannot be determined for either the Product or other
                  product(s) in such combination product, Net Sales for purposes
                  of determining royalty payments shall be calculated by
                  multiplying the Net Sales of the combination product by the
                  fraction C/(C+D) where C is the cost of manufacturing the
                  Product and D is the cost of manufacturing the other
                  product(s), determined in accordance with GAAP, consistently
                  applied.

         1.14.    "Product" means any human pharmaceutical product sold by
                  Sub-Licensees and/or its Affiliate and/or sub-sub-licensees to
                  a Third Party, the manufacture, use, importation or sale of
                  which in a specific country would in the absence of this
                  Agreement infringe an issued or granted claim in a Method of
                  Modulation Patent in such country and which was discovered or
                  developed by an activity which in

                                       3
   42
                  the absence of a license would infringe an issued or granted
                  claim in an Assay Patent.

         1.15.    "Sub-Licensee" means the party so identified and so above
                  named.

         1.16.    "Target" means a specific gene.

         1.17.    "Technology" means Materials, Intellectual Property, or both.

         1.18.    "Term" has the meaning set forth in Section 8.1.1.

         1.19.    "Third Party" means any entity other than (i) ABSC and any of
                  its Affiliates and (ii) Sublicensee and any of its Affiliates.

2.       SUBLICENSE

         2.1.     Sublicense Under the Methods of Modulation Patents.

                  2.1.1.   ABSC hereby grants to Sublicensee and its Affiliates,
                           for the specific Target listed in Exhibit B which is
                           neither (i) a Target for use in the field of
                           Cosmeceuticals which is excluded nor (ii) a Target
                           listed in Exhibit C, either as of the Effective Date
                           or within 12 months of the Effective Date, which also
                           is excluded, a non-exclusive, royalty-bearing,
                           worldwide license under the Method of Modulation
                           Patents to conduct research and development
                           concerning (but not to commercialize) one or more
                           compounds which are prospective Products directed
                           against such specific Target, and to make, use, have
                           made, sell, offer for sale, import, export, or
                           otherwise exploit any Product directed against such
                           specific Target, including treatment of humans with,
                           and in vivo administration for good laboratory
                           practice, preclinical development of, such
                           Products.

                  2.1.2.   ABSC shall within 30 days after entering into this
                           Agreement provide to OSI a copy thereof.


                                       4
   43
         2.2.     Right To Grant Subsublicenses Under The Method of Modulation
                  Patents.

                  2.2.1.   ABSC hereby grants Sublicensee the right to grant to
                           certain Third Parties and their Affiliates, for the
                           specific Target listed in Exhibit B a subsublicensee
                           under the Method of Modulation Patents to make, use,
                           have made, sell, offer for sale, import, export, or
                           otherwise exploit any Product directed against such
                           specific Target, including treatment of humans with,
                           and in vivo administration for good laboratory
                           practice pre-clinical development of, such products.

                  2.2.2.   Subsublicenses under Section 2.2.1. may be granted by
                           Sublicensee to any Third Party to which Sublicensee
                           has licensed or otherwise transferred its rights to
                           develop a Product directed against a specific Target
                           for which Sublicensee has a sublicense pursuant to
                           Section 2.1.1.; provided that Sublicensee's
                           obligations under this Agreement, including its
                           obligations under Section 3 shall continue and that
                           Sublicensee shall guarantee the performance by its
                           subsublicensee of all of subsublicensee's obligations
                           under any such subsublicense.

                  2.2.3.   Sublicensee shall within 30 days after entering into
                           any subsublicense under the Method of Modulation
                           Patents provide to ABSC and to OSI a copy thereof.

3.       COMPENSATION

         (ABSC, IN ADDITION TO THE PAYMENT SPECIFICALLY PROVIDED FOR IN THIS
         SECTION 3.1. MAY INCLUDE IN THIS SECTION 3 A PROVISION FOR AN UPFRONT
         SUB-LICENSING FEE.)

         3.1.     Compensation for Sublicenses Under the Method of Modulation
                  Patents.

                  3.1.1.   For the sublicenses granted to Sublicensee pursuant
                           to Section 2.1.1. for the specific Target listed in
                           Exhibit B Sublicensee will pay ABSC each year
                           commencing on the Effective Date of this Agreement
                           and on each anniversary date thereafter that such
                           sublicense is in effect, an annual license fee of
                           ________________ dollars ($_____ ).

                  3.1.2.   For the first Product directed against such Target
                           that reaches the following milestone events
                           Sublicensee will also pay ABSC within 30 days of such
                           milestone event the following amounts:


                                       5
   44
                                    Milestone Event              Payment  (US$)
                                    ---------------              -------  -----
                           i)  Upon filing an IND with the FDA         ________

                           ii) Upon acceptance of the filing of
                               an NDA by the FDA                       ________
                                    

                  3.1.3.   For such Target only one payment will be required for
                           each such milestone event regardless of the number of
                           Products directed against such Target for which
                           Sublicensee achieves such milestone events.

                  3.1.4.   For each Product directed against such Target
                           Sublicensee will also pay to ABSC a royalty of _____
                           percent (_%) of Net Sales of all such Products sold
                           by Sublicensee and its Affiliates and subsublicensees
                           on a country by country basis.

4.       ROYALTY PAYMENTS

         4.1.     Royalties payments due from Sublicensee to ABSC shall be paid
                  within sixty (60) days after the end of each calendar quarter
                  during which the royalty payment accrued. Each such payment
                  shall be accompanied by a statement certified by an officer of
                  Sublicensee with respect to each country indicating the amount
                  of the payment, the total Net Sales of each Product sold in
                  the country and the amount of royalty due.

         4.2.     To the extent that it is lawful and practicable to do so,
                  Sublicensee shall make all royalty payments required under
                  this Agreement in the United States of America in U.S.
                  Dollars. The royalty payments due on each sale made outside
                  the United States in a currency other than U.S. Dollars shall
                  be translated at the rate of exchange at which U.S. Dollars
                  are legally obtainable at Citibank, N.A. in New York, New
                  York, United States of America, for the currency of the
                  country in which the royalty payment is accrued on the last
                  business day of the calendar month in which the sale was made.
                  Sublicensee shall not be required to make any royalty payment
                  in contravention of the laws of any country, nor shall
                  Sublicensee be required to make the royalty payment in the
                  United States of America if Sublicensee is unable to recoup
                  the amount of such royalty or sublicense payment directly or
                  indirectly from the country in which the sales on which such
                  payment is based are made. In each country where the local
                  currency is blocked and cannot be removed from the country,
                  Sublicensee shall, at ABSC's request, pay the royalty payment
                  accrued in each such country to ABSC in local currency by
                  deposit to ABSC's account at a local bank designated by ABSC.

         4.3.     Sublicensee shall keep full and true books of account and
                  records of all sales of Product and Net Sales attributable to
                  sales by Sublicensee and its Affiliates and subsublicensees.
                  ABSC shall have the right, at ABSC's expense, through an
                  independent accountant reasonably approved by Sublicensee to
                  examine such 



                                       6
   45
                  books and records at any reasonable time during business hours
                  after notifying Sublicensee of its desire to do so. Such
                  examination shall be conducted no more often than once each
                  year and shall cover no more than the 3 preceding years. Such
                  independent accountant shall report only on the accuracy of
                  such books and records and the reports based thereon and shall
                  not disclose specific entries to ABSC.

5.       PROTECTION AND MAINTENANCE OF PATENT RIGHTS

         5.1.     Sublicensee acknowledges and agrees that OSI shall have
                  complete control, at its expense and within its sole
                  discretion, over the prosecution, maintenance and enforcement
                  of the Assay Patents and the Method of Modulation Patents.
                  ABSC directly, or through OSI, will provide Sublicensee with
                  written updates on the status of the prosecution of the Method
                  of Modulation Patents at least once per year.

6.       REPRESENTATIONS AND WARRANTIES

         6.1. Representations and Warranties of ABSC and Sublicensee.

                  As of the Effective Date each party hereby represents and
                  warrants:

                  Corporate Power. Such party is duly organized and validly
                  existing and in good standing under the laws of the state of
                  its incorporation and has all requisite corporate power and
                  authority to enter into this Agreement and to carry out the
                  provisions hereof.

                  Due Authorization. Such party is duly authorized to execute
                  and deliver this Agreement and to perform its obligations
                  hereunder.

                  Binding Agreement. This Agreement is a legal and valid
                  obligation binding upon it and enforceable in accordance with
                  its terms. The execution, delivery and performance of this
                  Agreement by such party does not conflict with any agreement,
                  instrument or understanding, oral or written, to which it is a
                  party or by which it may be bound, nor violate any law or
                  regulation of any court, governmental body or administrative
                  or other agency having jurisdiction over it.

                  Patents. Each party acknowledges and agrees that nothing in
                  this Agreement shall be construed as a warranty or
                  representation (i) as to the validity of any claim of a Method
                  of Modulation Patent or (ii) that any activity by Sublicensee
                  including the manufacture, use or sale of Product is, or will
                  be, free from infringement of patents of Third Parties.


                                       7
   46
         6.2.     Representations and Warranties of ABSC.

                  As of the Effective Date ABSC further represents and warrants
                  to Sublicensee that it has a license under the Method of
                  Modulation Patents and the right to grant the sublicense being
                  granted hereunder, subject to sub-licensees, representations
                  and warranties in Section 6.3 being correct and valid.

         6.3.     Representations and Warranties of Sublicensee.

                  As of the Effective Date Sublicensee further represents and
                  warrants to ABSC and to OSI that neither Sublicensee nor any
                  Affiliate of Sublicensee, prior to the Effective Date,
                  commenced good laboratory practice preclinical development of
                  a compound directed against such specific Target and which has
                  resulted from use of Aurora Technology or an Aurora Assay by
                  Sublicensee or an Affiliate of Sublicensee.

7.       CONFIDENTIALITY

         7.1.     Confidential Information. Except as expressly provided herein,
                  the parties agree that, for the Term and five (5) years
                  thereafter, the receiving party shall keep completely
                  confidential and shall not publish or otherwise disclose to
                  another party and shall not use for any purpose other than to
                  perform the purposes contemplated by this Agreement any
                  Confidential Information furnished to it by the disclosing
                  party hereto pursuant to this Agreement, except to the extent
                  that it can be established by the receiving party by competent
                  proof that such Confidential Information:

                  (i)      was already known to the receiving party, other than
                           under an obligation of confidentiality, at the time
                           of disclosure;

                  (ii)     was generally available to the public or otherwise
                           part of the public domain at the time of its
                           disclosure to the receiving party;

                  (iii)    became generally available to the public or otherwise
                           part of the public domain after its disclosure and
                           other than through any act or omission of the
                           receiving party in breach of this Agreement;

                  (iv)     was lawfully disclosed to the receiving party by a
                           person other than a party hereto, or

                  (v)      was independently developed by the receiving party.

         7.2.     Permitted Use and Disclosures. Each party hereto may use or
                  disclose Confidential Information disclosed to it by the other
                  party to the extent such use or disclosure is reasonably
                  necessary in filing or prosecuting patent applications,
                  prosecuting or defending litigation, complying with applicable
                  law, governmental regulation or court order, submitting
                  information to tax or other governmental authorities, making a
                  permitted sublicense or otherwise exercising its rights



                                       8
   47
                  hereunder, provided that if a party is required to make any
                  such disclosure of another party's Confidential Information,
                  it will give reasonable advance notice to the latter party of
                  such disclosure and, save to the extent inappropriate in the
                  case of patent applications, will use reasonable efforts to
                  secure confidential treatment of such information prior to its
                  disclosure (whether through protective orders or otherwise).

         7.3.     Confidential Terms. Except as expressly provided herein, each
                  party agrees not to disclose any terms of this Agreement to
                  another party other than OSI without the consent of the other
                  party; provided, however, each party reserves the right to
                  make reasonable disclosures as required by securities or other
                  applicable laws, or to actual or prospective investors or
                  corporate partners, or to accountants, attorneys and other
                  professional advisors on a need-to-know basis under
                  circumstances that reasonably ensure the confidentiality
                  thereof, or to the extent required by law. If such
                  Confidential information is to become public information by
                  such disclosure the disclosing party must obtain the written
                  consent of the non-disclosing party in order to obtain
                  protection of the Confidential Information if necessary.

8.       TERM AND TERMINATION

         8.1.1.   Unless terminated earlier, this Agreement and Sublicensee's
                  obligations to make payments to ABSC pursuant to Section 3.1.
                  is effective as of the Effective Date and shall continue in
                  full force and effect on a country by country basis until the
                  last expiration date of all patents encompassed within the
                  Method of Modulation Patents. ("Term").

         8.1.2.   Either party shall have the right to terminate this Agreement
                  at any time for a material breach of this Agreement by the
                  other party, provided that the nonbreaching party shall have
                  first given ninety (90) days prior written notice to the
                  breaching party describing such breach and stating the
                  nonbreaching party's intention to terminate this Agreement if
                  such breach remains uncured, and the breaching party
                  thereafter fails to cure such breach within such (90) days.

         8.1.3.   Sublicensee may terminate this Agreement by giving ABSC six
                  months' prior written notice of termination.

         8.1.4.   Termination of this Agreement shall not terminate either
                  party's obligations under Section 7, Sublicensee's obligations
                  to pay fees and royalties that have accrued under Section 3
                  prior to such termination or Sublicensee's obligations under
                  Section 9.3.


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   48
9.       MISCELLANEOUS

         9.1.     Binding Effect: Assignment. This Agreement shall be binding
                  upon the parties' respective successors and permitted assigns.
                  Neither party may assign this Agreement or any of its rights
                  or obligations hereunder without the prior written consent of
                  the other party (not to be unreasonably withheld) except that
                  either party may assign this Agreement as part of a merger or
                  consolidation in which the surviving entity assumes all of the
                  party's rights and obligations hereunder or a sale of
                  substantially all of the assets of such party to which this
                  Agreement relates.

         9.2.     Effect of Waiver. No waiver of any default, condition,
                  provisions or breach of this Agreement shall be deemed to
                  imply or constitute a waiver of any other default, condition,
                  provision or breach of this Agreement.

         9.3.     Indemnification. Each of ABSC and Sublicensee shall indemnify
                  and hold the other harmless with respect to any injury, loss
                  or cost resulting from the breach of any representation or
                  warranty provided pursuant to Section 6. Further, Sublicensee
                  shall indemnify and hold ABSC and OSI harmless with respect to
                  any injury, loss or cost resulting from the clinical testing
                  of compounds, the manufacture, use or sale of Products by
                  Sublicensee and its Affiliates and subsublicensees, and any
                  other activity carried out pursuant to the rights licensed
                  herein.

         9.4.     Force Majeure. Neither party shall lose any rights hereunder
                  or be liable to the other party for damages or losses (except
                  for payment obligations) on account of failure of performance
                  by the defaulting party if the failure is occasioned by war,
                  strike, fire, acts of God, earthquake, flood, lockout,
                  embargo, governmental acts or orders or restrictions, failure
                  of suppliers, or any other reason where failure to perform is
                  beyond the reasonable control and not caused by the negligence
                  or intentional conduct or misconduct of the nonperforming
                  party, and such party has exerted all reasonable efforts to
                  avoid or remedy such force majeure; provided, however, that in
                  no event shall a party be required to settle any labor dispute
                  or disturbance.

         9.5.     Amendment. No modification, supplement to or waiver of this
                  Agreement or any Addendum hereto or any of their provisions
                  shall be binding upon a party hereto unless (i) made in
                  writing, (ii) duly signed by an authorized representative of
                  both ABSC and Sublicensee, and (iii) consented to by OSI, such
                  consent not to be unreasonably withheld.

         9.6.     Entire Agreement. This Agreement, including the Exhibits
                  attached hereto, sets forth the entire understanding and
                  agreement of the parties as to the subject matter hereof, and
                  there are no other understandings, representations or
                  promises, written or verbal, not set forth herein or on which
                  either party has relied.

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         9.7.     Notices. All notices under this Agreement shall be given in
                  writing and shall be addressed to
                  the parties at the following addresses:

                  For Sublicensee:



                  For OSI:          OSI Pharmaceuticals, Inc.
                                    106 Charles Lindbergh Blvd.
                                    Uniondale, New York 11553
                                    Attn:  President

                  For ABSC:         Aurora Biosciences Corporation
                                    11010 Torreyana Road
                                    San Diego, California 92121
                                    Attn:  President

                  Copies of all notices sent by ABSC or Sublicensee shall be
                  sent to OSI.

                  Notices shall be in writing and shall be deemed delivered when
                  received, if delivered by a courier, or on the second business
                  day following mailing, if sent by first-class certified or
                  registered mail, postage prepaid, and return receipt
                  requested.

         9.8.     Arbitration. The parties recognize that disputes as to certain
                  matters may from time to time arise during the term of this
                  Agreement which relate to either party's rights and/or
                  obligations hereunder. It is the objective of the parties to
                  establish procedures to facilitate the resolution of disputes
                  arising under this Agreement in an expedient manner by mutual
                  cooperation without resort to arbitration. The parties agree
                  that prior to any arbitration concerning this Agreement,
                  ABSC's CEO and Sublicensee's CEO will meet in person or by
                  video-conferencing in a good faith effort to resolve any
                  disputes concerning this Agreement, such meeting to be held
                  within 30 days after notice is received by one party from the
                  other requesting such a meeting. Except as otherwise provided
                  specifically herein, any controversy or claim under this
                  Agreement except a claim as to the scope, validity or
                  enforcement of a claim of an Assay Patent or a Method of
                  Modulation Patent shall be settled solely by arbitration by
                  one arbitrator pursuant to the Commercial Arbitration Rules of
                  the American Arbitration Association (the "Association");
                  provided that the parties shall first have used their best
                  efforts to resolve such dispute by negotiation as set forth
                  above. The arbitration shall be conducted in ** The arbitrator
                  shall be selected by the joint agreement of the parties, but
                  if they do not so agree within twenty (20) days of the date of
                  a request for arbitration, the selection shall be made
                  pursuant to the rules of the Association. The decision reached
                  by the arbitrator shall be conclusive and binding upon the
                  parties hereto and may be filed with the clerk of any court of
__________

**   This portion has been redacted pursuant to a request for confidential 
     treatment.



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                  competent jurisdiction, and a judgment confirming such
                  decision may, if desired by any party to the arbitration, be
                  entered in such court. Each of the parties shall pay its own
                  expenses of arbitration and the expenses of the arbitrator(s)
                  shall be equally shared; provided, however, that if in the
                  opinion of the arbitrator(s) any claim hereunder or any
                  defense or objection thereto was unreasonable, the
                  arbitrator(s) may assess, as part of the award, all or any
                  part of the arbitration expenses (including reasonable
                  attorneys' fees) against the party raising such unreasonable
                  claim, defense or objection. Nothing herein set forth shall
                  prevent the parties from settling any dispute by mutual
                  agreement at any time.

         9.9.     Governing Law. This Agreement shall be governed by and
                  construed in accordance with the laws of the State of New
                  York, applicable to agreements made in New York without
                  regard, or giving effect, to its principles of conflict of
                  laws.

         9.10.    Severability. This Agreement is intended to be severable. If
                  any provision(s) of this Agreement are or become invalid, are
                  ruled illegal by a court of competent jurisdiction or are
                  deemed unenforceable under the current applicable law from
                  time to time in effect during the term hereof, it is the
                  intention of the parties that the remainder of the Agreement
                  shall not be affected thereby and shall continue to be
                  construed to the maximum extent permitted by law at such time.
                  It is further the intention of the parties that in lieu of
                  each such provision which is invalid, illegal, or
                  unenforceable, there shall be substituted or added as part of
                  this Agreement by such court of competent jurisdiction a
                  provision which shall be as similar as possible in terms of
                  the economic and business objectives intended by the parties,
                  to such invalid, illegal or unenforceable provision, but shall
                  be valid, legal and enforceable.

         9.11.    Independent Contractors. The parties hereto are acting as
                  independent contractors and shall not be considered partners,
                  joint venturers or agents of the other. Neither party shall
                  have the right to act on behalf of, or to bind, the other.

         9.12.    Headings. Captions and paragraph headings are for convenience
                  only and shall not form an interpretative part of this
                  Agreement. This Agreement shall not be strictly construed
                  against either party hereto and maybe executed in two or more
                  counterparts, each of which will be deemed an original.


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         IN WITNESS WHEREOF, the parties have executed this Agreement.

By:                                              Date:
   ---------------------------------                  -----------------------
Name:
Title:
For Sublicensee


By:                                              Date:
   ---------------------------------                  -----------------------

Timothy J. Rink M.D., Sc.D.
President, CEO and Chairman
For Aurora Biosciences Corporation


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